Exhaust system

ABSTRACT

An exhaust system includes a diesel oxidation catalyst (DOC) device mounted to an exhaust pipe for exhausting an exhaust gas of an engine and purifying hydrocarbon (HC) and carbon monoxide (CO) among the exhaust gas, an urea injector positioned at a rear of the diesel oxidation catalyst device for injecting an urea aqueous solution to an inside of the exhaust pipe, a mixer positioned at the rear of the urea injector, a diesel particulate matter filter (DPF) positioned at the rear of the mixer and coated with a catalyst devoid of a noble metal or a hydrolysis catalyst that does not oxidize ammonia and hydrolyzes the injected urea to reduce a particulate material of the exhaust gas, and a selective catalytic reduction (SCR) device positioned at the rear of the diesel particulate matter filter.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to Korean Patent Application No. 10-2016-0053376, filed with the Korean Intellectual Property Office on Apr. 29, 2016, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an exhaust system. More particularly, the present disclosure relates to an exhaust system in which a urea injection is possible at a high temperature, a performance of a selective catalytic reduction is improved and a self-diagnosis of an exhaust gas is eased.

BACKGROUND

In general, to reduce carbon monoxide (CO), hydrocarbon (HC), particulate matter (PM), nitrogen oxide (NOx) etc. as pollution materials contained in an exhaust gas, an exhaust system of an engine may include an exhaust gas post-treatment device such as a diesel oxidation catalyst (DOC) device, a diesel particulate matter filter (DPF), a selective catalytic reduction (SCR) device, and a nitrogen oxide storage catalyst (Lean NOx Trap, LNT catalytic) device, etc.

Referring to FIG. 4, a conventional exhaust system may include an engine 10, a diesel oxidation catalyst device 20, an urea injector 30, a mixer 40, a composite catalyst unit 55 (SDPF) and a selective catalytic reduction device 70. The conventional exhaust system may include a composite catalyst unit 55 at the rear of the mixer 40, and the composite catalyst unit 55 may have a shape such that the selective catalytic reduction coated to a high pore diesel particulate matter filter may be exposed to a high temperature when regenerating the composite catalyst unit 55 for a soot combustion. Since the selective catalytic reduction may be degraded by the high temperature, a maximum soot trapped amount must be controlled to be a predetermined amount or less before the regenerating soot combustion. That is, to prevent the degradation, a soot mass limit (SML) must decrease such that a regeneration period of the composite catalyst unit 55 is shorted, and the fuel consumption is deteriorated.

The composite catalyst unit 55 as the high pore diesel particulate matter filter (a pore rate of 50% or more) has a low heat resistance and many pore, such that the trapping efficiency is lower compared with the conventional diesel particulate matter filter, thereby being a disadvantage regarding the soot trapping. Also, in the structure of the composite catalyst unit 55, a low pressure exhaust gas regeneration device, and the selective catalytic reduction device 70 may be sequentially disposed, the partial flow may be again supplied to the combustion chamber by the low pressure exhaust gas regeneration (LP-EGR) pipe 60 such that it is a disadvantage regarding the exhaust gas self-diagnosis (On-Board Diagnotics; OBD). Also, to combust the trapped soot, when an exhaust temperature is increased through an engine post-injection, there may not be a purification function of hydrocarbon and carbon monoxide of the generated excess amount.

On the other hand, in a conventional exhaust system shown in FIG. 5, in the case of the system that the diesel oxidation catalyst device 20 and the diesel particulate matter filter 55 are disposed at an engine compartment CC, at the rear of the diesel oxidation catalyst device 20, the urea injector 30, the mixer 40, and the selective catalytic reduction device 70 are disposed at a vehicle lower part thereof, or uf, the exhaust gas self-diagnosis by the nitrogen oxide sensors 72 and 74 at the front and rear of the selective catalytic reduction device 70 is possible. However, since the urea injector 30 is mounted at the vehicle lower part thereof, or uf, and the urea is injected at a position that the exhaust temperature is low, the injection is restricted to low temperatures and the entirely low purification performance appears.

Also, at the vehicle lower part thereof, or uf, to uniform supply ammonia (NH3) to the selective catalytic reduction device 70 through the urea injection, a predetermined distance is required between the urea injector 30, the mixer 40, and the selective catalytic reduction device 70 at the vehicle lower part thereof, or uf. That is, a space for thermal decomposition, hydrolysis, and a mixing of the urea is required. If the urea injector and the mixer are all disposed at the vehicle lower part thereof, or uf, the space may be limited to ensure the volume of the selective catalytic reduction device 70.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

SUMMARY

An exemplary embodiment of the present disclosure provides an exhaust system in which the diesel oxidation catalyst device, the urea injector, mixer, and the diesel particulate matter filter are positioned at the engine compartment, the catalyst without, or devoid of, a noble metal or a hydrolysis catalyst is coated to the diesel particulate matter filter, and the selective catalytic reduction device is only mounted at the vehicle lower part is provided.

An exhaust system according to exemplary embodiment of the present disclosure may include a diesel oxidation catalyst (DOC) device mounted to an exhaust pipe formed to exhaust an exhaust gas of an engine for purifying hydrocarbon (HC) and carbon monoxide (CO) among the exhaust gas; an urea injector positioned at a rear of the diesel oxidation catalyst device for injecting an urea aqueous solution to an inside of the exhaust pipe; a mixer positioned at the rear of the urea injector and provided to enable a rapid flow diffusion of the exhaust gas passing through the diesel oxidation catalyst device; a diesel particulate matter filter (DPF) positioned at the rear of the mixer and coated with a catalyst devoid of a noble metal or a hydrolysis catalyst that does not oxidize ammonia and hydrolyzes the injected urea to reduce a particulate material of the exhaust gas; and a selective catalytic reduction (SCR) device positioned at the rear of the diesel particulate matter filter for reducing the nitrogen oxide of the exhaust gas passing through the diesel particulate matter filter.

A low pressure exhaust gas regeneration (LP-EGR) device pipe may be connected between the diesel particulate matter filter and the selective catalytic reduction device.

The exhaust system according to an exemplary embodiment of the present disclosure may further include an ammonia oxidation catalyst (AOC) device positioned at the rear of the selective catalytic reduction device for oxidizing ammonia (NH₃) of the exhaust gas passing through the selective catalytic reduction device and reducing the nitrogen oxide.

A nitrogen oxide sensor may be provided at the front and the rear of the selective catalytic reduction device.

A nitrogen oxide sensor may be provided between the diesel oxidation catalyst device and the urea injector and between the diesel particulate matter filter and the selective catalytic reduction device.

The diesel oxidation catalyst device, the urea injector, the mixer, and the diesel particulate matter filter may be positioned at an engine compartment CC of the vehicle, and the selective catalytic reduction device may be positioned at a vehicle lower part uf.

The exhaust system according to an exemplary embodiment of the present disclosure may further include an injection chamber as a part of the exhaust pipe connecting the diesel oxidation catalyst device and the diesel particulate matter filter and forming a space where the reduction agent is injected by the urea injector.

An exhaust system according to another exemplary embodiment of the present disclosure may include a nitrogen oxide storage catalyst (lean NOx trap; LNT) device for absorbing and storing a nitrogen oxide generated by a lean combustion of an engine and for reducing the nitrogen oxide into nitrogen by a reduction action to be exhausted; an urea injector positioned at a rear of the nitrogen oxide storage catalyst device for injecting an urea aqueous solution inside the exhaust pipe; a mixer positioned at the rear of the urea injector and provided to enable a rapid flow diffusion of the exhaust gas passing through the nitrogen oxide storage catalyst device; a diesel particulate matter filter (DPF) positioned at the rear of the mixer and coated with a catalyst devoid of a noble metal or a hydrolysis catalyst that does not oxidize ammonia and hydrolyzes the injected urea to reduce a particulate material of the exhaust gas; and a selective catalytic reduction (SCR) device positioned at the rear of the diesel particulate matter filter for reducing the nitrogen oxide of the exhaust gas passing through the diesel particulate matter filter.

A low pressure exhaust gas regeneration device pipe may be connected between the diesel particulate matter filter and the selective catalytic reduction device.

The exhaust system according to another exemplary embodiment of the present disclosure may further include an ammonia oxidation catalyst device positioned at the rear of the selective catalytic reduction device for oxidizing ammonia of the exhaust gas passing through the selective catalytic reduction device, and reducing the nitrogen oxide.

A nitrogen oxide sensor may be provided at the front and the rear of the selective catalytic reduction device.

A nitrogen oxide sensor may be provided between the nitrogen oxide storage catalyst device and the urea injector and between the diesel particulate matter filter and the selective catalytic reduction device.

The nitrogen oxide storage catalyst device, the urea injector, the mixer, and the diesel particulate matter filter may be positioned at an engine compartment of the vehicle, and the selective catalytic reduction device may be positioned at a vehicle lower part.

The exhaust system according to another exemplary embodiment of the present disclosure further includes an injection chamber as a part of the exhaust pipe connecting the nitrogen oxide storage catalyst device and the diesel particulate matter filter and forming a space where the reduction agent is injected by the urea injector.

According to the present disclosure, by providing the urea injector and the mixer at the engine compartment, the urea injection is possible at the high temperature and the uniform mixing of the exhaust gas is possible.

Also, the general diesel particulate matter filter without the selective catalytic reduction is provided and the diesel particulate matter filter is not coated with the noble metal such that the oxidation of ammonia is prevented.

Also, ammonia is supplied until the selective catalytic reduction device of vehicle lower part by injecting the urea at the engine compartment such that the flow uniformity of ammonia is high by the mixing of the exhaust gas and the selective catalytic reduction device of larger volume may be ensured at the vehicle lower part.

Also, the selective catalytic reduction device or the selective catalytic reduction device, and the ammonia oxidation catalyst device are provided at the vehicle lower part, and the nitrogen oxide sensor is mounted at the front and the rear of the catalyst device such that the urea injection control and the exhaust gas self-diagnosis are possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of an exhaust system according to an exemplary embodiment of the present disclosure.

FIG. 2 is a schematic block diagram of an exhaust system according to another exemplary embodiment of the present disclosure.

FIG. 3 is a graph showing a result measuring an exhaust temperature depending on time for each position of a vehicle.

FIG. 4 is a schematic block diagram of a conventional exhaust system.

FIG. 5 is a schematic block diagram of another conventional exhaust system.

DETAILED DESCRIPTION

The present disclosure will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the disclosure are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present disclosure.

Further, in exemplary embodiments, since like reference numerals designate like elements having the same configuration, a first exemplary embodiment is representatively described, and in other exemplary embodiments, only configurations different from the first exemplary embodiment will be described.

The drawings are schematic, and are not illustrated in accordance with a representative scale. Relative dimensions and ratios of portions in the drawings may be illustrated to be exaggerated or reduced in size for clarity and convenience, and the dimensions are merely exemplary, and are not limiting. In addition, like structures, elements or components illustrated in two or more drawings may use like reference numerals for showing similar features. It will be understood that when an element such as a layer, film, region or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present.

An embodiment of the present disclosure shows an exemplary embodiment of the present disclosure in detail. As a result, various modifications of the drawings can be expected. Therefore, the exemplary embodiment is not limited to a specific aspect of the illustrated region, and for example, includes modifications of an aspect by manufacturing.

An exhaust gas purification device according to an exemplary embodiment of the present disclosure will be described with reference to FIG. 1 to FIG. 3.

FIG. 1 is a schematic view showing an exhaust gas purification device according to an exemplary embodiment of the present disclosure.

Referring to FIG. 1, the exhaust system may be connected with an engine 10 to purify the exhaust gas of the engine 10 and include a diesel oxidation catalyst device 20, a urea injector 30, a mixer 40, a diesel particulate matter filter 50 and a selective catalytic reduction device 70.

The diesel oxidation catalyst device 20 may be mounted to an exhaust pipe 5 formed to exhaust the exhaust gas of the engine 10. That is, the front of the diesel oxidation catalyst device 20 may be connected with the engine 10 to receive the exhaust gas exhausted from the engine 10. Here, the front and the rear of the constituent element are based on the flow of the exhaust gas and it is defined that the exhaust gas flows from the front to the rear of the constituent elements.

The diesel oxidation catalyst device 20 is a device where a carrier is provided inside a predetermined case and the diesel oxidation catalyst is coated to the carrier. The diesel oxidation catalyst device 20 oxidizes hydrocarbon and carbon monoxide in the exhaust gas through the diesel oxidation catalyst.

The diesel particulate matter filter 50 may be formed the catalyst carrier to trap the particulate material included in the exhaust gas and the particulate material is purified through a chemical conversion process. That is, the diesel particulate matter filter 50 is a device for physically trapping the particulate material among the exhaust gas of the diesel engine 10 by using the filter and increasing the exhaust gas temperature of the particulate material above an ignition temperature of 550 degrees after driving by a predetermined distance to combust the particulate material, thereby reducing a pollution material. In the diesel particulate matter filter 50, a pressure sensor or a temperature sensor may be provided at the front and the rear of the diesel particulate matter filter 50, and the sensors may sense the pressure and the temperature after and before the exhaust gas passes through the diesel particulate matter filter 50. An electronic control unit (ECU) may thereby control the engine 10 and related devices to remove the particulate material.

The diesel particulate matter filter 50 may be coated with the catalyst without a noble metal (platinum (Pt), palladium (Pd), rhodium (Rh)). Since the noble metal is not coated thereon, ammonia of the exhaust gas inflowing to the diesel particulate matter filter 50 may be prevented from being oxidized. Also, the diesel particulate matter filter 50 may be coated with the hydrolysis catalyst for hydrolyzing the urea injected from the urea injector 30. The hydrolysis catalyst does not oxidize nitrogen, but hydrolyzes the sprayed urea. In the composite catalyst unit (SDPF) used in the conventional exhaust system, the selective catalytic reduction (SCR) may be coated to the high pore diesel particulate matter filter, and thereby the selective catalytic reduction may be degraded by a high temperature when exposed to the high temperature. Accordingly, the regeneration period of the composite catalyst unit is shortened and the deterioration of the fuel consumption may be caused, in the present exemplary embodiment, instead of the composite catalyst unit, the catalyst without the noble metal is coated or the filter coated with the hydrolysis catalyst for removing the particulate material is used, thereby enhancing the regeneration period and the fuel consumption.

In the conventional exhaust system, as shown in FIG. 4, as the selective catalytic reduction (SCR) includes the composite catalyst unit 55 coated to the high pore diesel particulate matter filter, the partial flow of the exhaust gas is again supplied to the combustion chamber through the low pressure exhaust gas regeneration device pipe 60, and the flow amount exited into the low pressure exhaust gas regeneration device may be confirmed such that the exhaust gas self-diagnosis is difficult. However, according to exemplary embodiments of the present disclosure, instead of the composite catalyst unit, the diesel particulate matter filter coated with the catalyst without the noble metal or coated with the hydrolysis catalyst is provided. Accordingly, the flow of the exhaust gas may be confirmed by the nitrogen oxide sensor of the front and rear of the selective catalytic reduction device such that the exhaust gas self-diagnosis is possible.

The selective catalytic reduction device 70 may be provided at the rear of the diesel oxidation catalyst device 20. The selective catalytic reduction device 70 may function by converting the reduction agent (the urea) into ammonia by the heat of the exhaust gas and reducing the nitrogen oxide into a nitrogen gas and a water as the catalyst reaction of the nitrogen oxide and the ammonia among the exhaust gas by the selective catalytic reduction.

The nitrogen oxide sensors 72 and 74 may be provided at the front and rear of the selective catalytic reduction device 70, thereby measuring the nitrogen oxide amount after and before the exhaust gas passes through the selective catalytic reduction device 70.

The urea injector 30 may be positioned at the rear of the diesel oxidation catalyst device 20 and injects the urea aqueous solution to the inside of the exhaust pipe 5. The urea injector 30 may inject the urea and may directly inject ammonia. Also, other reduction agents besides ammonia may be injected along with ammonia.

The mixer 40 may be positioned at the rear of the urea injector 30 to enable the rapid flow diffusion of the exhaust gas passing through the diesel oxidation catalyst device 20.

The low pressure exhaust gas regeneration device pipe 60 may be connected between the diesel particulate matter filter 50 and the selective catalytic reduction device 70 such that the exhaust gas passing through the diesel particulate matter filter 50 may be recycled to the engine 10 through the exhaust gas regeneration device. The exhaust gas regeneration device recycles the part of the exhaust gas exhausted after the combustion of the fuel in the engine 10 to an intake device of the engine 10 to be again inflowed to the combustion chamber of the engine 10. As a consequence, an air-fuel mixture decreases in density without a change in the air-fuel ratio of the air-fuel mixture, thus lowering the combustion temperature.

That is, the exhaust gas regeneration device supplies the part of the exhaust gas to the intake system of the engine 10 to inflow it to the combustion chamber when it is necessary to reduce the exhaust amount of the nitrogen oxide depending on the driving state of the engine 10. By doing so, exhaust gases, which are insert gases whose volume does not change, contribute to decrease the density of the mixture to a lower level, and therefore decrease the flame propagation velocity during fuel combustion. This suppresses an increase in combustion temperature and slows the fuel combustion, thereby suppressing the generation of nitrogen oxides.

The diesel oxidation catalyst device 20, the urea injector 30, the mixer 40 and the diesel particulate matter filter 50 may be provided at the engine compartment CC of the vehicle, and the selective catalytic reduction device 70 may be provided at the vehicle lower part uf.

By providing the urea injector 30 and the mixer 40 at the engine compartment CC, the urea injection is possible at the high temperature and the uniform mixing of the exhaust gas is possible. Also, since the urea is injected from the engine compartment CC and ammonia is supplied till the selective catalytic reduction device 70 of the vehicle lower part uf, the flow uniformity of ammonia is high by the mixing of the exhaust gas, and the selective catalytic reduction device 70 of the further larger volume may be ensured at the vehicle lower part uf.

FIG. 2 is a block diagram schematically showing an exhaust system according to another exemplary embodiment of the present disclosure.

As shown in FIG. 2, in the exhaust system according to another exemplary embodiment of the present disclosure, differently from the exhaust system according to an exemplary embodiment of the present disclosure referring to FIG. 1, a nitrogen oxide storage catalyst device (LNT) 20 may be included instead of the diesel oxidation catalyst device.

The nitrogen oxide storage catalyst device 20 may absorb and store the nitrogen oxide generated by a lean combustion of the engine 10 and reduce the nitrogen oxide into nitrogen by the reduction action to be exhausted, and the urea injector 30 injecting the urea aqueous solution inside the exhaust pipe 5 is provided at the rear of the nitrogen oxide storage catalyst device 20.

The mixer 40 to enable the rapid flow diffusion of the exhaust gas passing through the nitrogen oxide storage catalyst device 20 may be provided at the rear of the urea injector 30, and the diesel particulate matter filter 50 for reducing the particulate material of the exhaust gas and the selective catalytic reduction device 70 for reducing the nitrogen oxide of the exhaust gas passing through the diesel particulate matter filter 50 may be disposed at the rear of the mixer 40.

Like the above-described exemplary embodiment, the diesel particulate matter filter 50 in the present exemplary embodiment may be also coated with a catalyst without a noble metal or may be coated with a hydrolysis catalyst for hydrolyzing the urea.

The urea injector 30, the mixer 40, and the selective catalytic reduction device 70 provided in the exhaust system according to the present exemplary embodiment may be the same as that of the above-described exemplary embodiment, such that a repeated description will be omitted.

As shown in FIG. 2, nitrogen oxide sensors 72 and 74 may be provided between the nitrogen oxide storage catalyst device 20 and the urea injector 30 and between the diesel particulate matter filter 50 and the selective catalytic reduction device 70. The nitrogen oxide amount may be measured before and after the exhaust gas passes through the mixer 40 and the diesel particulate matter filter 50.

An injection chamber 35 connecting the nitrogen oxide storage catalyst device 20 and the diesel particulate matter filter 50 and forming the space where the reduction agent is injected by the urea injector 30 may be further included as a part of the exhaust pipe 5. The reduction agent injected inside the injection chamber 35 may be uniformly mixed by the mixer 40 provided in the injection chamber 35, and the exhaust gas and the reduction agent rapidly flow into, and are diffused into, the diesel particulate matter filter 50 connected to the rear of the injection chamber 35.

In the exemplary embodiment described in FIG. 1, the injection chamber may be also provided to be connected to the diesel oxidation catalyst device 20 and the diesel particulate matter filter 50, and the reduction agent injected in the injection chamber 35 may be uniformly mixed by the mixer 40 provided in the injection chamber 35.

Also, between the diesel particulate matter filter 50 and the selective catalytic reduction device 70, the low pressure exhaust gas regeneration device pipe 60 may be disposed and connected. Thereby, the exhaust gas passing through the diesel particulate matter filter 50 may be recycled to the engine 10 through the exhaust gas regeneration device.

An ammonia oxidation catalyst (AOC) device 80 for oxidizing ammonia of the exhaust gas passing through the selective catalytic reduction device 70 and reducing the nitrogen oxide may be further included at the rear of the selective catalytic reduction device 70.

The ammonia oxidation catalyst device 80 may function by preventing ammonia from being directly emitted into the atmosphere. This is to prevent air pollution by an ammonia slip phenomenon, where the reduction agent does not participate in the reaction and is directly exhausted into the atmosphere when the reduction agent is excessively injected to ensure the high selective catalytic reduction efficiency.

The ammonia oxidation catalyst may be a copper-contained zeolite impregnated with the noble metal, or an iron-contained zeolite impregnated with the noble metal, or a copper impregnated with the noble metal or a silicon containing alumina catalyst composition.

The nitrogen oxide storage catalyst device 20, the urea injector 30, the mixer 40, and the diesel particulate matter filter 50 may be provided at the engine compartment CC of the vehicle, and the selective catalytic reduction device 70 may be provided at the vehicle lower part uf.

FIG. 3 is a graph showing a result measuring an exhaust temperature depending on time for each position of a vehicle.

Referring to FIG. 3, an exhaust temperature for the urea injection must reach 180 degrees or more at a minimum. In this case, the engine compartment CC, in which the diesel oxidation catalyst device 20 and the diesel particulate matter filter 50 are positioned, reaches the exhaust temperature of 180 degrees or more after about 150 seconds or more such that the rapid urea injection is possible. However, in the vehicle lower part uf in which the selective catalytic reduction device 70 is positioned, the exhaust temperature reaches to 180 degrees after about 800 seconds. Accordingly, to perform the urea injection in the vehicle lower part uf, the time of about 800 seconds or more is required. Accordingly, it is an advantage that the urea injection is performed in the engine compartment that reaches the high temperature earlier.

As described above, according to exemplary embodiments of the present disclosure, by providing the urea injector and the mixer in the engine compartment, the urea injection is possible at the high temperature and the uniform mixing of the exhaust gas is possible.

Also, the general diesel particulate matter filter without the selective catalytic reduction is provided and the noble metal is not coated to the diesel particulate matter filter, thereby ammonia is prevented from being oxidized.

Also, since ammonia is supplied to the selective catalytic reduction device of the vehicle lower part by injecting the urea in the engine compartment, the flow uniformity of ammonia is high by the mixing of the exhaust gas, and the selective catalytic reduction device of the larger volume may be ensured in the vehicle lower part.

Also, the selective catalytic reduction device or the selective catalytic reduction device, and the ammonia oxidation catalyst device are provided in the vehicle lower part, and the nitrogen oxide sensor is mounted at the front and rear of the catalyst device such that the urea injection control and the exhaust gas self-diagnosis are possible.

While this disclosure has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

What is claimed is:
 1. An exhaust system comprising: a diesel oxidation catalyst (DOC) device mounted to an exhaust pipe for exhausting an exhaust gas of an engine and purifying hydrocarbon (HC) and carbon monoxide (CO) among the exhaust gas; an urea injector positioned at a rear of the diesel oxidation catalyst device for injecting an urea aqueous solution to an inside of the exhaust pipe; a mixer positioned at the rear of the urea injector for enabling a rapid flow diffusion of the exhaust gas passing through the diesel oxidation catalyst device; a diesel particulate matter filter (DPF) positioned at the rear of the mixer and coated with a catalyst devoid of a noble metal or a hydrolysis catalyst that does not oxidize ammonia and hydrolyzes the injected urea to reduce a particulate material of the exhaust gas; and a selective catalytic reduction (SCR) device positioned at the rear of the diesel particulate matter filter for reducing the nitrogen oxide of the exhaust gas passing through the diesel particulate matter filter.
 2. The exhaust system of claim 1, wherein a low pressure exhaust gas regeneration (LP-EGR) device pipe is connected between the diesel particulate matter filter and the selective catalytic reduction device.
 3. The exhaust system of claim 1, further comprising an ammonia oxidation catalyst (AOC) device positioned at the rear of the selective catalytic reduction device for oxidizing ammonia (NH₃) of the exhaust gas passing through the selective catalytic reduction device and reducing the nitrogen oxide.
 4. The exhaust system of claim 1, wherein a nitrogen oxide sensor is provided at the front and the rear of the selective catalytic reduction device.
 5. The exhaust system of claim 1, wherein a nitrogen oxide sensor is provided between the diesel oxidation catalyst device and the urea injector and between the diesel particulate matter filter and the selective catalytic reduction device.
 6. The exhaust system of claim 1, wherein the diesel oxidation catalyst device, the urea injector, the mixer, and the diesel particulate matter filter are positioned in an engine compartment CC of the vehicle, and the selective catalytic reduction device is positioned at a vehicle lower part uf.
 7. The exhaust system of claim 1, further comprising an injection chamber as a part of the exhaust pipe connecting the diesel oxidation catalyst device and the diesel particulate matter filter, and forming a space where the reduction agent is injected by the urea injector.
 8. An exhaust system comprising: a nitrogen oxide storage catalyst (lean NOx trap; LNT) device for absorbing and storing a nitrogen oxide generated by a lean combustion of an engine and reducing the nitrogen oxide into nitrogen by a reduction action to be exhausted; an urea injector positioned at a rear of the nitrogen oxide storage catalyst device for injecting an urea aqueous solution inside the exhaust pipe; a mixer positioned at the rear of the urea injector for enabling a rapid flow diffusion of the exhaust gas passing through the nitrogen oxide storage catalyst device; a diesel particulate matter filter (DPF) positioned at the rear of the mixer and coated with a catalyst devoid of noble metal or a hydrolysis catalyst that does not oxidize ammonia and hydrolyzes the injected urea to reduce a particulate material of the exhaust gas; and a selective catalytic reduction (SCR) device positioned at the rear of the diesel particulate matter filter for reducing the nitrogen oxide of the exhaust gas passing through the diesel particulate matter filter.
 9. The exhaust system of claim 8, wherein a low pressure exhaust gas regeneration device pipe is connected between the diesel particulate matter filter and the selective catalytic reduction device.
 10. The exhaust system of claim 8, further comprising an ammonia oxidation catalyst device positioned at the rear of the selective catalytic reduction device for oxidizing ammonia of the exhaust gas passing through the selective catalytic reduction device and reducing the nitrogen oxide.
 11. The exhaust system of claim 8, wherein a nitrogen oxide sensor is provided at the front and the rear of the selective catalytic reduction device.
 12. The exhaust system of claim 8, wherein a nitrogen oxide sensor is provided between the nitrogen oxide storage catalyst device and the urea injector and between the diesel particulate matter filter and the selective catalytic reduction device.
 13. The exhaust system of claim 8, wherein the nitrogen oxide storage catalyst device, the urea injector, the mixer, and the diesel particulate matter filter are positioned in an engine compartment of a vehicle, and the selective catalytic reduction device is positioned at a vehicle lower part.
 14. The exhaust system of claim 8, further comprising an injection chamber as a part of the exhaust pipe connecting the nitrogen oxide storage catalyst device and the diesel particulate matter filter and forming a space where the reduction agent is injected by the urea injector. 